1. Field of the Invention
The present invention relates to a diffusion pipe and a method for cleaning the diffusion pipe.
2. Description of the Related Art
Diffusion pipes are widely used in a wastewater treatment device and the like, where such a diffusion pipe includes a tubular-shaped membrane body made of a viscoelastic material and a tubular membrane support body that supports the membrane body from inside of the membrane body, and the membrane body has diffusion slits cutting therethrough between an outer peripheral surface and an inner peripheral surface thereof.
Japanese Utility Model Publication No. H01-25679 (Y2) discloses a diffusion pipe in which an air pipe main body is provided with several holes, and a rubber tube having a number of cut holes is fit onto the pair pipe main body in order to prevent untreated wastewater from flowing backward into the diffusion pipe and clogging the diffusion slits. The holes are formed on a peripheral surface, including a side surface, of the air pipe main body constituting the diffusion pipe, and the diffusion slits formed as the cut holes are provided all over the membrane body.
Japanese Patent Laid-Open Application No. 2005-334847 discloses a diffusion pipe in which a tubular core member is made of a resin having one or more air-spouting holes evenly distributed on one side thereof, and a tubular air diffusion member formed of a porous membrane rubber or the like covers the core member. Air spouts from the air-spouting holes provided on one side of the core member, flows through a space between the core member and the air diffusion member, and then is discharged from the minute pores of the air diffusion member.
Japanese Patent No. 4781302 discloses a diffusion pipe in which an air pipe having a plurality of aeration openings is mounted on a base end of a tube base member, and an elastic film having slits on its peripheral portion covers the tube base member and the air pipe, such that the air is discharged through the slits. Similarly to the diffusion pipe of Japanese Patent Laid-Open Application No. 2005-334847, the air spouted from the aeration openings provided on one end of the diffusion pipe flows through a space between the tube base member and the elastic film, and then is discharged from the slits of the elastic film.
A diffusion pipe having such a structure that a membrane body formed of a tube-shaped viscoelastic body is fitted from outside onto a tubular membrane support body is supposed not to have a backflow problem in which sludge comes in through the diffusion slits formed on the membrane body. However, in reality, as the membrane body repeatedly expands and contracts in accordance with the air flowing through a space between the membrane support body and the membrane body, some of the sludge may flow in through the diffusion slits during such process. When the elasticity of the membrane body deteriorates as it ages and the amount of the sludge flowing in increases, the risk of clogging the diffusion slits also increases.
In addition, since the membrane body of such conventional diffusion pipes described above have diffusion slits formed all over including an area facing the through-holes formed on the membrane support body, most of the air supplied from the through-holes is spouted right away through the diffusion slits in the vicinity of the through-holes, thereby the diffusion becomes disadvantageously uneven along the axis direction of the diffusion pipe. In addition, the diffusion slits near the through-holes tend to lose the elasticity by opening widely, thereby undesirably increase the risk of pulling in the sludge when they open.
When the diffusion slits are clogged to a certain extent so as to decrease the air diffusion efficiency, a cleaning process is conducted in order to recover the air diffusion efficiency by supplying a cleaning solution into the membrane support body and cleans the diffusion slits. However, if the cleaning solution still remains inside the membrane support body when the air is supplied after the cleaning process, such residual cleaning solution interferes with emission of the air through the through-holes, thereby preventing a quick recovery of the air diffusion efficiency even after the diffusion slits have been cleaned.